Recording media such as an optical disk, a magneto-optical disk, and a phase change optical disk are arranged such that, in data tracks thereon, the address to be absolute location information is recorded in some way. A disk drive unit corresponding to the disks carries out recording/reproduction, etc. in such a way that the address on the data tracks is detected so that the judgment that whether or not the unit reaches a desired location of the tracks is made, and if it is confirmed that the unit reaches the desired location, the disk drive unit starts the operation of recording/reproduction.
As illustrated in FIG. 14, the above-identified disks adopt, for instance, an address recording pattern arranged such that an address area and data are recorded in one sector corresponding to a unit of data to which one address value is assigned. According to this recording pattern, each of the sectors formed on the disk is physically divided into areas so as to store the address information and the data. What are recorded as the address information are an actual address value AD and a CRC error detecting code attached to the same. FIG. 14 exemplifies a recording pattern in which both of the address value AD and the CRC error detecting code are recorded only once. However, these two may be recorded more than once to reduce the address read error.
As FIG. 15 illustrates, an address information detecting apparatus for acquiring address information from the disk using the above-mentioned address recording pattern includes: an address detecting section 101; a CRC error detecting section 102; an address keeping section 103; a selector 104; an address information keeping section 105; an interpolation address generating section 106; and an interpolation address keeping section 107.
The address detecting section 101 is a sort of address decoder for decoding the address information recorded in the disk, and the decoded address information is recorded in a register of the address keeping section 103. The decoded address information is sent to the CRC error detecting section 102 along with the CRC error detecting code, so as to be subjected to the detection (error detection) of an error bit, as the address. The output of the address keeping section 103 and the output of the CRC error detecting section 102 are supplied to the selector 104.
The selector 104 receives an interpolation address from the interpolation address keeping section 107. This interpolation address is generated by interpolating the immediately preceding address information of the selector 104 into the current address information. If the result of the detection in the CRC error detecting section 102 is error-free, the selector 104 selects the address information supplied from the interpolation address keeping section 103 so as to output the same. In contrast, if the result includes an error, the selector 104 outputs the interpolation address supplied from the interpolation address keeping section 107. The output from the selector 104 is supplied to the address information keeping section 105, and as detected address information, the output is supplied to a recording/reproduction operation block, etc. (not illustrated) so as to be utilized for the operation of recording/reproduction.
The address information kept in the address information keeping section 105 is supplied to the interpolation address generating section 106 as well. This interpolation address generating section 106 determines the address of the next sector, and this address is supplied to the interpolation address keeping section 107. The output of the interpolation address keeping section 107 is, as described above, supplied to the selector 104.
By means of the above-mentioned process, it is possible to detect the address information of the disk in which the address value and the error detecting code are recorded in the address area.
A method of recording (i) an address value and (ii) an error correcting code which can correct the error of the address value both in the address area is disclosed by Japanese Laid-Open Patent Publication No. 11-31365/1999 (Tokukaihei 11-31365; published on Feb. 2, 1999).
As a method of recording the address and the error correcting code which can correct the error of the address value both in the address area, as illustrated in FIG. 16, there is a method arranged such that one sector corresponding to a unit of data to which one address value is assigned is physically divided into areas so that the address information and the data are recorded therein. In this method, an actual address AD and an error correcting code ECC attached to this address AD are recorded as the address information. Incidentally, the error correcting code ECC stores a non-binary BCH code and a binary BCH code.
FIG. 17 illustrates an arrangement in which the non-binary BCH code is utilized, as an example of the address information detecting apparatus for acquiring the address information from the disk with the above-mentioned address recording pattern.
In the address information detecting apparatus illustrated in FIG. 17, first of all, address data supplied as a series of 1 bits is converted to parallel data in a serial-parallel conversion section 108. Then the decoded address as parallel data is supplied to (i) a register of an address keeping section 109 and (ii) a syndrome calculation section 110. The syndrome calculation section 110 calculates a syndrome for detecting an error in the supplied address, the result of the calculation is supplied to an address correction section 111 so that the existence of the error is examined, and the result of the examination is supplied to a selector 113. Using the syndrome calculated in the syndrome calculation section 110, the address correction section 111 judges whether or not the error can be corrected, and the result is sent to the selector 113. If the error correction is possible according to the judgment, the error of the address supplied from the address keeping section 109 is corrected.
The selector 113 receives an interpolation address supplied from an interpolation address keeping section 116, in addition to the address information from the address keeping section 109 and the corrected address information from a corrected address keeping section 112. This interpolation address is generated by interpolating the subsequent address information by the current address information supplied from the selector 113, in an interpolation address generating section 115.
If no error is detected by the output from the syndrome calculation section 110, the selector 113 supplies the input data, which is from the address information keeping section 109, to the address information keeping section 105. This input data is supplied as the address information. In contrast, if the error is detected and the correction thereof is judged to be possible according to the input from the address correction section 111, as the address information, the input data from the corrected address keeping section 112 is supplied to the address information keeping section 105. If the error is detected but the correction thereof is judged to be impossible, the interpolation address supplied from the interpolation address keeping section 116 is supplied to the address information keeping section 105, as the address information.
Thanks to the sequences above, it is possible to detect the address information of the disk in which the address value and the error correcting code are recorded in the address area.
However, the conventional address information detecting method described above has the following problems.
That is, the error detection by the conventional address information detecting method is based on the judgment such that the occurrence of the error is acknowledged when a received word is not properly coded.
For instance, as FIG. 18 illustrates, a received word y is constituted by codewords (wi and wj) with a minimum distance of dmin and errors not more than d. y is located inside a small sphere which is centered at wi and has a radius d, and hence if the following equation (1) holds,dmin≦d+1  (1) there are no other codewords within the radius d. Thus y does not correspond to other codewords so that the occurrence of the error is acknowledged in the receiving end.
In other words, if the number of errors does not satisfy the equation (1), the errors cannot be detected so as to be overlooked.
Now, as FIG. 19 illustrates, assume that a received word y is constituted by codewords (wi and wj) with a minimum distance of dmin and t errors.
In this case, if t satisfies the following equation (2), there are no other codewords inside a small sphere having a radius of t.dmin≧2t+1  (2) 
Thus, since wi is the codeword most similar to y, y is corrected so that wi substitutes for y.
Also in this case, if the number of errors does not satisfy the equation (2), the errors are not properly corrected so that an improper codeword is used for the substitution.
As described above, the conventional address information detecting method cannot avoid the mis-detection or mis-correction when the number of errors does not satisfy the equations (1) or (2) in the respective case of the error detection or the error correction.
On this account, even if the detection of the address information is carried out with the assistance of the error detecting code and the error correcting code, the mis-detection and mis-correction still occur when a certain number of errors are included. Moreover, even if the error correction is successfully carried out or the result of the detection indicates error-free, the address could be mis-detected so that there is a possibility of malfunction, etc. of the apparatus, provided that the mis-detected address information is carelessly adopted.
In this manner, the mis-detection and mis-correction of the address are unavoidable in the cases of the error detection and the error correction, and hence when the mis-detection or mis-correction of the address occurs, the conventional address information detecting apparatus wrongly adopts the mis-corrected address or the error address which is overlooked, and according to such addresses, the operation of the apparatus is controlled. On this account, the apparatus mis-recognizes the absolute location information on the disk so that the operation of recording/reproduction by the apparatus is not properly carried out, and in the worst case the apparatus malfunctions.